Added error when not exporting any namespaces for GIR
Added error when not exporting any namespaces for GIR

https://bugzilla.gnome.org/show_bug.cgi?id=669551

Distrotech/vala,GNOME/vala,frida/vala,GNOME/vala,rvu95/vala,frida/vala,xdave/pvala,spidermonkdust/vala,Distrotech/vala,rvu95/vala,flobrosch/vala-fixes,rvu95/vala,severinh/vala,playya/vala,severinh/vala,spidermonkdust/vala,frida/vala,Distrotech/vala,GNOME/vala,frida/vala,flobrosch/vala-fixes,tjol/vala-tjol,tjol/vala-tjol,spidermonkdust/vala,playya/vala,jessevdk/vala,GNOME/vala,flobrosch/vala-fixes,playya/vala,tjol/vala-tjol,jessevdk/vala,jessevdk/vala,frida/vala,severinh/vala